Systems and methods for tissue healing

ABSTRACT

Systems, methods and devices are provided for use in a negative pressure wound therapy system for healing a wound in a patient. Various aspects may include an ester-based material adapted to be directly applied to the wound, such as a smooth muscle fistula, without substantially damaging tissue in the wound during dressing changes. The ester-based material may have an affinity for the wound bed surface and/or wound fluid. In addition various aspects may include a device adapted to close the wound, such as a smooth muscle fistula.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a national stage application, and claims priority toand the benefit of International Application No. PCT/US2015/015968 filedon Feb. 13, 2015, which claims the benefit of U.S. ProvisionalApplication No. 61/940,245 filed Feb. 14, 2014, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND

Negative pressure wound therapy is a therapeutic technique used topromote healing and closure of various types of acute or chronic woundsin the human body. Negative pressure wound therapy is a wound bedmanagement technique that creates an environment of sub-atmosphericpressure over the wound bed to draw fluid out of the wound. The effectof the sub-atmospheric pressure environment is to reduce inflammationand increase blood flow within the wound, providing a more oxygen richenvironment to the wound and improve the delivery of wound-healing whiteblood cells, proteins, carbohydrates, and growth factors.

Generally, the wound is irrigated with saline and/or antibiotics, andmay be covered with a non-adherent material that adapts to the contoursof the wound. An absorptive dressing is applied over the non-adherentmaterial and an occlusive material is applied over the dressed wound toform an air-tight seal. A vacuum tube is connected to an opening in theocclusive material. A vacuum pump applied to the vacuum tube providesthe negative pressure needed to draw fluid through the wound forcollection and removal. The non-adherent material and/or the absorptivedressing may be changed according to various factors such as the amountof fluid output from the wound, the patient's age, clinical objectives,and the like.

The absorptive dressing may include any one of a number of materialsthat are chosen as a function of the type of wound, clinical objectives,and the comfort of the patient. For example, the absorptive dressing mayinclude cotton gauze for shallow wounds such as pressure sores ordiabetic ulcers of the skin. The absorptive dressing may include a foammaterial for open cavity wounds such as gunshot wounds, leg ulcers, andsurgically created cavities. These wounds may be lightly, moderately, orheavily exuding wounds that may benefit from the high absorptioncapacity of foam material. The foam material may be cut to fit themargins of the open cavity wound and placed inside the wound.Conventional foam materials generally have pore diameters in the rangeof approximately 100 μm-600 μm and are consistently used with aprotective layer, typically petrolatum gauze, between the foam materialand the wound bed in wounds involving fistulas, tendons, nerves orsensitive tissues.

SUMMARY

Various embodiments of the invention provide dressings, systems andmethods for a negative pressure wound therapy system for healing a woundin a patient. Dressings, systems and methods according to variousaspects of the present invention may include an ester-based materialadapted to be directly applied to the wound, such as a smooth musclefistula, without substantially damaging tissue in the wound duringdressing changes. The ester-based material may have an affinity for thewound bed surface and/or wound fluid. Under pressure, the ester-basedmaterial may promote uniformity of wound fluid movement through thewound and dressing and regulate temperature within the wound.

In addition, systems and methods according to various aspects of thepresent invention may include a device adapted to close a wound such asa smooth muscle fistula.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be derived byreferring to the detailed description when considered in connection withthe following illustrative figures. In the following figures, likereference numbers refer to similar elements and steps throughout thefigures.

Elements and steps in the figures are illustrated for simplicity andclarity and have not necessarily been rendered according to anyparticular sequence or scale. For example, steps that may be performedconcurrently or in different order are illustrated in the figures tohelp to improve understanding of embodiments of the present invention.In addition, graphical representations of structural features have beensimplified for the purposes of illustration.

The figures described are for illustration purposes only and are notintended to limit the scope of the present disclosure in any way.Various aspects of the present invention may be more fully understoodfrom the detailed description and the accompanying drawing figures,wherein:

FIG. 1 schematically illustrates a simplified cross-section of anegative pressure wound therapy treatment system including an absorptivedressing according to an embodiment of the present invention;

FIG. 2 schematically illustrates a simplified cross-section of anegative pressure wound therapy treatment system including an integralvacuum according to another embodiment of the present invention;

FIG. 3A schematically illustrates cell sacrifice in relation to the poresize of a conventional absorptive dressing;

FIG. 3B schematically illustrates cell sacrifice in relation to the poresize of the absorptive dressing of the embodiment of FIGS. 1 and 2;

FIG. 4 schematically illustrates a detailed pore structure of theabsorptive dressing of the embodiment of FIGS. 1 and 2;

FIGS. 5A-5C schematically illustrate simplified cross-sections ofabsorptive dressings with various pore sizes and/or multiple layersaccording to further embodiments of the absorptive dressing of FIGS. 1and 2;

FIG. 6 schematically illustrates a simplified cross-section of anotherembodiment of a negative pressure wound therapy treatment systemincluding an absorptive dressing having preformed flow paths to directwound fluid flow;

FIG. 7A schematically illustrates a simplified cross-section of afurther embodiment of a negative pressure wound therapy treatment systemincluding an absorptive dressing having barriers to direct wound fluidflow;

FIG. 7B representatively illustrates a simplified cross-section of abarrier of FIG. 7A;

FIG. 8A schematically illustrates a simplified cross-section of afurther embodiment of a negative pressure wound therapy treatment systemincluding an absorptive dressing having a radial housing to direct woundfluid flow;

FIG. 8B representatively illustrates a simplified perspective view ofthe radial housing of FIG. 8A;

FIG. 8C representatively illustrates a simplified cross-sectional viewof the radial housing of FIG. 8B;

FIG. 8D representatively illustrates a simplified cross-sectional viewof the radial housing of FIG. 8C along line I-I′;

FIG. 9 schematically illustrates a simplified cross-sectional view of anegative pressure wound therapy treatment system including a healinglayer that may be incorporated into the embodiments of the negativepressure wound therapy treatment system.

DETAILED DESCRIPTION

The present invention may be described in terms of functional blockcomponents and various processing steps. Such functional blocks may berealized by any number of components configured to perform the specifiedfunctions and achieve the various results. For example, the presentinvention may employ various process steps, apparatuses, systems,methods, etc. In addition, the present invention may be practiced inconjunction with any number of systems and methods for treating openwounds. Further, the present invention may employ any number ofconventional techniques for wound treatment, wound bed preparation,treating or preventing infection of wounds, reducing inflammation,extracting fluid from wounds, changing wound dressings, and preventingthe advancement of wound edges.

The particular implementations shown and described are illustrative ofthe invention and its best mode and are not intended to otherwise limitthe scope of the present invention in any way. Indeed, for the sake ofbrevity, conventional manufacturing, connection, preparation, and otherfunctional aspects of the system may not be described in detail.Furthermore, the connecting lines shown in the various figures areintended to represent examples of functional relationships and/or stepsbetween the various elements. Many alternative or additional functionalrelationships or physical connections may be present in a practicalsystem.

The terms “comprises”, “comprising”, “includes” or “including” or anyvariation thereof, are intended to reference a non-exclusive inclusion,such that a process, method, article, composition, system, or apparatusthat comprises a list of elements does not include only those elementsrecited, but may also include other elements not expressly listed orinherent to such process, method, article, composition, system, orapparatus.

Expressions such as “at least one of,” when preceding a list ofelements, modify the entire list of elements and do not modify theindividual elements of the list. Further, the use of “may” whendescribing embodiments of the present invention refers to “one or moreembodiments of the present invention.”

When a first element is described as being “coupled” or “connected” to asecond element, the first element may be directly “coupled” or“connected” to the second element, or one or more other interveningelements may be located between the first element and the secondelement.

Spatially relative terms, such as “beneath”, “below”, “lower”,“downward”, “above”, “upper” and the like, may be used herein for easeof description to describe one element or feature's relationship toanother element(s) or feature(s) as illustrated in the figures. It willbe understood that the spatially relative terms are intended toencompass different orientations of the device in use or operation inaddition to the orientation depicted in the figures. For example, if thedevice in the figures is turned over, elements described as “below” or“beneath” other elements or features would then be oriented “above” theother elements or features. Thus, the exemplary term “below” canencompass both an orientation of above and below. The device may beotherwise oriented (rotated 90 degrees or at other orientations) and thespatially relative descriptors used herein interpreted accordingly.

It will be understood that, although the terms “first”, “second”,“third”, etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondiscussed below could be termed a second element, component, region,layer or section, without departing from the spirit and scope of theinventive concept.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the singular forms “a”, “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise.

As used herein, the term “substantially,” “about,” and similar terms areused as terms of approximation and not as terms of degree, and areintended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art.

Various representative implementations of the present invention may beapplied to any area of damaged tissue on the body of a human or animal.In some embodiments, the damaged tissue may include a penetrating woundthat may expose underlying tissue where wound closure is desired. In oneembodiment, the present invention may be applied to incisional wounds.The penetrating wound may also include wounds caused by surgery and/ortrauma, fistulas including smooth muscle fistulas, lacerations, thermalinjuries such as burns, chemical wounds, electrical wounds, and thelike. For example, the damaged tissue may include one or more fistulas.Fistulas may result from various traumas, including gunshot wounds,Caesarean sections, Crohn's disease, and various other diseases,injuries or surgery. Fistulas can occur between two epithelializedsurfaces, such as blood vessels, skin, intestines or other holloworgans. One type of commonly occurring fistula is an enterocutaneousfistula, which occurs between the intestine and the skin surface.However, the present invention is not limited thereto, and may beapplied to a various types of fistulas, including other fistulas of thedigestive system or fistulas located in other systems of the body.

In some embodiments, various representative implementations of thepresent invention may be applied to any system for promoting healing ofa wound bed including smooth muscle tissue. Certain representativeimplementations may include, for example, any suitable system or methodfor providing an at least partially or fully occlusive wound dressingfor the treatment and healing of fistulas in smooth muscle tissue usingnegative pressure wound therapy. In one embodiment, a negative pressurewound therapy system may include an absorptive dressing applied directlyin contact with the wound bed for absorbing wound fluid. In someembodiments, one or more of a healing layer may optionally be applied toa wound bed including smooth muscle tissue beneath the absorptivedressing and may further encourage wound closure and healing. Thehealing layer may be overlaid with the absorptive dressing for absorbingwound fluid from the wound bed. An occlusive seal may overlay theabsorptive dressing and the wound edge. A vacuum pump may be coupled toa vacuum tube that may be connected to the occlusive seal withcommunication of the negative pressure through the absorptive dressingto the wound bed. Activation of the vacuum pump may cause withdrawal ofthe wound fluid from the wound bed into the absorptive dressing forremoval with dressing changes.

A smooth muscle fistula may be an open cavity wound including exposedsmooth muscle tissue. Unlike cardiac and skeletal muscle, which includefirm and relatively coarse tissue, smooth muscle is fragile, friable,and easily damaged or stripped when touched with a foreign object.Negative pressure wound therapy using any conventional absorptivedressing such as foam or gauze are contraindicated in the treatment ofcertain fistulas due to the fragile nature of, for example, cardiactissue, nerve tissue, tendon, exposed blood vessels, and smooth muscletissue. Specifically, the clinical standard of practice does not allowdirect contact of the foam or gauze or any conventional absorptivedressing to any wound including smooth muscle because such directcontact is known to cause damage to smooth muscle tissue, aggravatingthe wound and preventing healing. Without being bound by theory, it isbelieved that such systems inappropriately draw wound fluidnon-uniformly from the fistula, increase the down growth of tissue intothe wound, and cause undesirable cell sacrifice during dressing changes.For at least these reasons, fistulas are generally treated withmechanical attempts to close the wound by methods such as suturing,gluing, and/or stapling the fistula closed. Such mechanical woundclosures have marginal success in promoting the healing of fistulas.

Referring to FIG. 1, a negative pressure treatment system 100 mayinclude an absorptive dressing 101. In one embodiment, the absorptivedressing 101 may be placed in direct contact with a wound bed 120. Thewound bed 120 may include smooth muscle tissue 121 surrounding a smoothmuscle fistula 122. The absorptive dressing 101 may also contact varioustissues 123 adjacent to the fistula 122 and in the wound bed 120,including skeletal and smooth muscle tissue, bone (not shown), and othertissues. An occlusive material 130 may overlay the absorptive dressing101 and adhere to skin 124 flanking the edges 125 of the wound bed 120.The application of the occlusive material 130 may provide an airtightseal over the wound bed 120. The occlusive material 130 may include anysuitable airtight material, such as plastic. In one embodiment, anadapter 131 may be coupled to the occlusive material 130 to provide anaccess point through the occlusive material 130 for the passage of gasor wound fluid while maintaining the airtight seal of the occlusivematerial 130 over the wound bed 120. A conventional vacuum tubeconnector 132 may be coupled to the adapter 131. A vacuum tube 133 maybe coupled to the vacuum tube connector 132 and to a vacuum pump 134.The vacuum pump 134 may include any suitable conventional vacuum pumpused with negative pressure therapy systems such as a piezoelectricpump, a sound wave pump, and/or a mechanical pump. Such conventionalvacuum pumps may be capable of applying negative pressure in the amountof 0-200 mm Hg. Activation of the vacuum pump 134 may provide a reducedpressure environment over the wound bed 120.

In use, medical personnel, such as a doctor, may apply the absorptivedressing 101 directly to the wound bed, which includes the smooth musclefistula 122. Wound fluid may begin to be absorbed into the absorptivedressing 101. An occlusive material 130 may be overlaid on theabsorptive dressing 101 such that it fully covers the edges 125 of thewound bed 120. Medical personnel may then exert pressure on theocclusive material 130 until it adheres to the skin 124 and creates anairtight seal over the wound bed 120. The adapter 131 may be connectedto a source of negative pressure, for example, a vacuum pump 134. Thevacuum pump 134 may be assembled with the vacuum tube connector 132 andthe vacuum tube 133 in order to connect to the adapter 131. The adapter131 may also be connected to the access point in the occlusive material130 to allow negative pressure to flow from the vacuum pump 134 to theabsorptive dressing 101. Upon activating the vacuum pump 134, negativepressure may be applied to the absorptive dressing 101 therebywithdrawing wound fluid from the absorptive dressing 101 and the woundbed 120.

In the alternative embodiment of FIG. 2, a negative pressure treatmentsystem 200 may include a vacuum pump 234 integrated into the absorptivedressing 101. In this embodiment, the vacuum tube 133 or vacuum tubeconnector 132 may not be needed. The integral vacuum pump 234 may allowa patient with the smooth muscle fistula 122 to have improved freedom ofmovement or allow the patient to be fully ambulatory while using thenegative pressure treatment system 100. Such movement may be restrictedwhen the vacuum tube 133 is connected to the external vacuum pump 134 asshown in FIG. 1. This embodiment functions similar to the embodiment ofFIG. 1, however, medical personnel need not assemble a separate vacuumtube connector, vacuum tube or adapter in order to apply negativepressure to the absorptive dressing 101.

In various embodiments of the present invention, the absorptive dressing101 may include any biocompatible absorptive material suitable fordirect contact with wounds, such as wounds including smooth muscle. Inone embodiment, the biocompatible absorptive material may have anaffinity for living tissue and/or wound fluid. The wound fluid mayinclude exudate, transudate, extracellular matrix, blood, and/or anyother type of fluid coming from the wound having a variety ofviscosities. In some embodiments, the biocompatible absorptive materialmay be capable of absorbing and/or suspending wound fluid having thevariety of viscosities. In some embodiments, the biocompatible materialmay be adapted to contact smooth muscle 121 without causing substantialcellular disruption or damage in a reduced pressure environment and/orduring dressing changes. In some embodiments, the absorptive dressing101 may include an ester-based material.

The ester-based material may be formed into a foam suitable for trimmingto fit the boundaries of the wound bed 120, such as fitting to the edges125. The ester-based material may include ester functional groups thatmay be exposed to and/or directly contact the surface of the smoothmuscle 121. The ester functional group is a carboxylic acid derivativehaving the general chemical formula

Esters may be derived from an inorganic acid or organic acid in which atleast one —OH (hydroxyl) group is replaced by an —O-alkyl (alkoxy)group. The carbonyl oxygen of the ester functional group may have apartial negative charge with a delocalized carbocation. The esterfunctional group may be capable of at least three chemical reactions.First, the electrophilic carbocation may be vulnerable to nucleophilicattack by another molecule, such as hydroxide, resulting in addition ofthe nucleophile to the carbocation. Such nucleophilic attack may resultin hydrolysis of the ester. Second, an electrophile may be accepted bythe highly electronegative carbonyl oxygen. The electrophile may be ahydrogen ion. Accordingly, the carbonyl oxygen may participate inintermolecular hydrogen bonding. Third, the carbon adjacent to thecarbocation may undergo deprotonation by a base and leave a negativecharge on the adjacent carbon or the carbonyl oxygen, as stabilized byresonance structures.

In various embodiments, any one or more of these ester functional groupreactivities may participate in the affinity of the ester-based materialfor living tissue and/or the wound fluid, in particular when applieddirectly to the smooth muscle tissue 121. The ester functional group mayhave an affinity for a variety of molecules in the wound bed 120,including polar groups on cells in the wound bed 120 such as thephospholipid bilayer of cell membranes, the water component of woundfluid produced by the wound bed 120, and the water component of fluidcoming through the smooth muscle fistula 122, such as intestinal fluid.

As described above, the ester functional groups may interact with thesmooth muscle tissue 121 through hydrogen bonding, nucleophilicaddition, including hydrolysis, and/or base deprotonation. Without beingbound by theory, it is believed that these chemical interactions mayform along the interface between the absorptive dressing 101 and thesmooth muscle tissue 121, evenly spreading a lifting force of negativepressure over the exposed surface of the smooth muscle tissue 121,creating a consistent and uniform pull upward.

At least one or more of the presence of the chemical interaction of thetissue in the wound bed 120 with the ester functional groups of theabsorptive dressing 101 and/or the interface layer 902 (discussed withrespect to FIGS. 8A-8B below) and negative pressure from the vacuum pumpmay promote a uniform upward and/or inward pull of the wound bed 120. Asa result of this uniform pull upward and/or inward, the ester-basedmaterial may produce little to no detrimental changes or damage to thegeometric environment of the wound bed 120, may promote the uniformmovement of wound fluid through the wound bed 120, and may reduce theflow of wound fluid out of the wound bed 120. The reduction of fluidand/or the pull of tissue inward may lead to closure and healing of thewound bed 120.

The reactivity of the ester functional group with the smooth muscletissue 122 in combination with the negative pressure environmentprovided by the vacuum pump 134 may have a variety of effects on thewound bed 120. Without being bound by theory, it is believed that theester functional group may promote at least one or more of: an optimalgeometric environment of the wound, the formation of granulation tissue,temperature regulation, at least partial reversal of tissue downgrowth,optimal fluid management, and induction of cell growth.

The geometric environment of the wound bed 120 impacts certainphysiological phenomenon including the migration of cells, such asepithelial cell growth and capillary endothelial cell migration, and themovement of exudate through the wound carrying growth factors,nutrients, and proteins. As discussed further below, without being boundby theory, non-uniform movement of wound fluid can lead to the poolingof wound fluid at the wound bed. This pooling may disrupt cell-to-cellinteractions and may lead to cell distortion or damage. It is believedthat the ester-based material limits such cellular distortions andmaintains an optimal or improved geometric environment for wound healingand closure. This may be due to the chemical interactions of the esterfunctional groups with the tissue of the wound bed 120.

Granulation tissue may include new connective tissue and the formationof new blood vessels on the surface of the wound bed 120, facilitatingthe healing process. The growth of granulation tissue may fill the woundbed 120 and assist in closure of the wound and/or the reduction ofexudate output. The application of the ester-based material to the woundbed 120 including the smooth muscle fistula 122 may stimulate tissuegranulation.

Maintaining a normal temperature in the wound bed 120 may preventvasoconstriction and hypoxia and may decrease the risk of infection. Thesmall pore diameter 111 of the ester-based material which provides aneven distribution and movement of the exudate throughout the absorptivedressing 101 may effectively regulate the normal temperature of thewound bed 120 by reducing evaporation and/or uneven airflow through theester-based material. Evaporation and/or uneven airflow, such as thatexhibited by ether-based materials, may cause the wound temperature todrop which may increase tissue metabolism and decrease pH. These changesin the wound tissue metabolism and pH may cause bleeding, disruption ofgranulation tissue formation, and pain for the patient.

The absorptive dressing 101 including the ester-based material incombination with continuous or intermittent negative pressure mayprovide enhanced temperature regulation of the wound bed 120. In variousembodiments of the present invention, the ester-based material mayprovide temperature regulation in one or more locations on theester-based material. First, the interface between the surface of theester-based material and the tissue of the wound bed 120 where the esterfunctional groups make direct contact and react with the tissue mayconsistently maintain a substantially normal body temperature. Second,the remaining portion of the ester-based material may evenly distributeand interact with the exudate pulled from the wound bed 120, formingchemical bonds such as hydrogen bonds with the exudate as the exudatemoves through the ester-based material towards the source of negativepressure. The exudate in the ester-based material may establish atemperature equilibrium which may be lower than body temperature and mayprovide a layer of insulation over the ester-based material to tissueinterface. As described above, effective regulation of the temperatureof the wound bed may positively affect healing providing an optimaltemperature for cellular metabolism and pH maintenance. Additionally,the ester-based material may provide a thermal buffer to increase thetemperature of incoming instillation fluids such as saline that may beapplied to the negative pressure treatment system 100, such as for theaddition of antibiotics to the wound, and may prevent or reduce a lowtemperature shock to the wound bed 120.

The chemical interactions of the ester functional groups in theester-based material with the tissue of the wound bed 120 may result inimproved fluid management as compared to non-ester based materials. Theevenly distributed affinity of the ester functional groups for thetissue and exudate may allow exudate to move through the wound in aneven and orderly manner toward the source of negative pressure, despitethe effect of microstrain distortions of the surface of the wound bed120 in response to the negative pressure. This affinity may promoteconsistent collection of exudate fluid in folds and contouring lines ofthe wound bed 120. The effect of the uniform movement of exudateprovides efficient removal of exudate, fluids, and materials andpromotes the uniform orientation of cell growth throughout the surfaceof the wound bed 120. Without being bound by theory, the uniformaffinity of the ester functional groups may also prevent or decrease theformation of cavities or undermined tissues due to the closer connectionbetween the tissue and the ester-based material. Further, the uniformaffinity of the ester functional group for the tissue may require lesscellular work to orient and re-orient during physical movements of thepatient and changes in the negative pressure treatment system 100. Thus,systems used in the industry, such as the instillation of externalfluids, soak, vacuum pause cycles, and/or dressing changes, to abateissues of fluid pooling may not be as necessary or may lead to evenfurther improved results when used with the ester-based material.

An upward pull induced by the interaction of the ester functional groupswith the tissue on the surface of the wound bed 120 may reduce and/or atleast partially reverse naturally occurring tissue down growth into thewound bed 120. Down growth of epithelial tissue and deeper tissue intothe wound bed 120 may occur naturally in incisions and wounds. However,an upward pull provided by the ester-based material on the wound bed 120may uniformly distribute pressure over the surface of the wound bed 120and cause migrating cells to move toward the surface of the wound bed120.

In one embodiment, the ester-based material may be a polymer ofpolyurethane, specifically polyester. As compared to conventionalether-based foams, ester-based foams are more rigid, have a smalleropen-reticulated cell structure, and have a higher tensile strength.Ester-based foams also suspend moisture substantially evenly and allowfluid to flow evenly throughout the foam due to its small cell structureand/or chemical affinity for moisture.

Conventional foams are typically ether-based foams, including polymersof polyether triol, and have a larger pore diameter. Without being boundby theory, it is believed that these relatively large pore sizes, ascompared to the sizes of individual cells with which the foam materialwas used, such as smooth muscle cells, are responsible for the damagecaused to wound beds when conventional foam material is placed in directcontact with the wound. FIG. 3A representatively illustrates an exampleof pore diameters 311 of conventional foam materials 301 compared tosmooth muscle cells 321.

In addition, without being bound by theory, it is believed that thelarge pore diameter of ether-based foams reduces the foam's ability tosuspend moisture and allow moisture to pass through the foam easily. Theease of movement of moisture through the ether-based foam has thepractical result of promoting fluid collection in the portion of thefoam having the lowest center of gravity, leading to an unevendistribution of moisture throughout the ether-based foam. The poorability of ether-based foams to retain moisture renders theminappropriate for use in negative pressure therapy applications becausethe ether-based foam provides inadequate temperature regulation to thewound bed, poor delivery of additives to the wound bed such asantibiotics, and limits ambulation of a patient due to the unevendistribution and pooling of moisture in a sealed system when the patientmoves.

Additionally, the basic chemical structure of the ether linkage inether-based polyurethane foams is R—O—R′. The central oxygen may besubstantially unreactive, incapable of appreciable hydrogen bonding, andsignificantly less polar than the oxygen of ester functional groups.Without being bound by theory, it is believed that the stability of theether linkage renders them incapable of forming the same types ofchemical interactions or reactions as ester-based foams includinghydrolysis and reactions with acids, oxidizing agents, reducing agents,bases, and active metal species. The chemical and resultant structuraldifferences between ether-based foams and ester-based foams impact theperformance of these materials in different applications. In healingapplications using negative pressure therapy systems, the temperatureregulation and even distribution of moisture provided by the variousembodiments of the ester-based material described may optimize woundhealing and closure.

The absorptive dressing 101 including the ester-based material may bemanufactured and/or further processed to obtain any desired physicalproperties. In some embodiments, the desired physical properties mayoptimize pore size and structure such as pore density, pore geometry,pore reticulation, permeability of pores to wound fluid, dry tensilestrength, and/or wet tensile strength. Processing of the ester-basedmaterial may further optimize the ability of the ester-based material tomaintain a saturated volume of suspended fluid. For example, theester-based material of the absorptive dressing 101 applied to the woundbed 120 may ultimately become saturated with wound fluid coming throughthe smooth muscle fistula 122. Wound fluid may be continually removedfrom the absorptive dressing 101 through the vacuum tube 133 and, at thesame time, wound fluid may continually be entering the absorptivedressing 101 from the smooth muscle fistula 122. As a result of theester-based material's affinity for the wound fluid, a saturatedabsorptive dressing 101 may allow a substantially equal volume of woundfluid and/or number of wound fluid molecules into the ester-basedmaterial as is exiting the ester-based material through the vacuum tube133. Accordingly, wound fluid removal may not substantially affect thesaturated volume of wound fluid retained by the absorptive dressing 101under clinically relevant negative pressures of 0-200 mm Hg. Withoutbeing bound by theory, it is believed that this environment where thevolume in is substantially equal to the volume out (referred to simplyat times as a “one molecule in/one molecule out” environment) asprovided by a substantially saturated absorptive dressing 101 promotes aplurality of benefits to wound healing such as effective temperatureregulation, even distribution of negative pressure, and maintaining aneven distribution of wound fluid despite movement of the patient.

In other applications, the geometry of the pores of the absorptivedressing 101 may include a shape that provides for increased surfacearea inside the pores 110, such as a round shape. Such increased surfacearea may increase contact of the ester functional groups with the woundbed 120 and may benefit the healing of the smooth muscle fistula 122.The increased surface area may be particularly beneficial for a woundwith a high wound fluid flow, such as an intestinal fistula. In otherembodiments, the geometry of the pores 110 of the absorptive dressing101, shown in FIG. 3B, may be configured to correlate with the generalshape of the primary cell type in the wound bed 120, such as epithelialcells, skeletal muscle cells, and/or smooth muscle cells. In addition,the pores may be configured to correlate with the size and/or diameterof any of the cells or other material of the exudate from the wound bed.For example, the pores 110 may have an elongated shape to correlate withthe elongated dimensions of skeletal or smooth muscle cells. Exampledimensions and shapes of cell types that may be in the wound bed areshown in Table 1 below. The pores 110 may be configured to correlatewith the diameter, shape and/or length of any of the cells types below,in addition to the diameter, shape and/or length of other cell types inthe wound bed 120. However, the pores 110 may have a variety of shapes,including octagonal, hexagonal, diamond or trigonal.

TABLE 1 General Cell Type Cell Shape Diameter Length MUSCLE CELLS variesvaries varies Cardiac Muscle Cells Short, 10 μm-15 μm 80 μm-100 μmnarrow cell Smooth Muscle Cells Short, 0.2 μm-2 μm   20 μm-200 μmelongate, fusiform cell Skeletal Muscle Cells Large,  10 μm-100 μm Up to100 cm elongate cell EPITHELIAL CELLS varies varies varies (includingendothelial cells) CONNECTIVE varies varies varies TISSUES NERVE CELLSvaries varies varies

In some applications, the pore diameter and/or size of the absorptivedressing 101 may be customized to promote the interaction of the porestruts with the cells in the wound bed 120. For example, the porediameter and/or size may be substantially equivalent to the diameterand/or size of a primary cell type in the wound bed 120. In someembodiments, the pore width may be about 0.1 μm to about 100 μm, inorder to correlate with the size of smooth muscle cells. In otherembodiments, the pore width may be about 0.1 μm to about 50 μm.

Without being bound by theory, it is believed that reducing the size ofthe pores 110 to be substantially equivalent to the diameter of smoothmuscle cells leads to a reduction in cell sacrifice, as representativelyillustrated in FIGS. 3A-3B. An example of pore 310 s of a conventionalether-based foam 301 is illustrated in FIG. 3A. Pores 310 may have adiameter 311 of about 400 μm to about 600 μm. In general, smooth musclescells 321 adjacent to pores 310, shown in the illustration of a portionof a wound bed 320, may be removed (e.g., sacrificed) during dressingchanges. Without being bound by theory, it is believed that thesacrifice of cells 321 may be caused by the formation of weakcell-to-cell contacts, such as cell junctions, that form as damagedtissue regrows to fill a wound bed 120. The struts or edges of pores 310in conventional ether-based foams may contact some smooth muscle cells321 and destroy weak cell junctions formed as the smooth muscle cells321 divide as part of wound healing. Pore 110 of the ester-based foam ofan embodiment of the present invention may be illustrated in FIG. 3B. Insome embodiments, pore 110 may have a diameter of about 30 μm or lessand be close to the diameter of a smooth muscle cell. As a result, thepores 110 may make many contacts along the length of each smooth musclecell 121. In this fashion, it is believed that the pores 110 mayfunction as a scaffold to support closer and/or stronger cell junctionsas the smooth muscles cells 121 divide. The smooth muscle cells 121 maytherefore remain intact during dressing changes, with no appreciableloss of the smooth muscle cells 121 at the foam-tissue interface thatmay disrupt wound healing.

Referring to FIG. 4, in various embodiments of the present invention,the size of the pores 110 in the absorptive dressing 101 including theester-based material may be adapted to reduce the sacrifice of thesmooth muscle tissue 121. In one embodiment, the size of pores 110 maybe reduced to any pore size that is less than the pore size ofconventional ester-based foam of approximately 100 μm-600 μm. In someembodiments, the pore diameter 111 may be substantially equivalent tothe diameter of smooth muscle cells. Smooth muscle cells include short,elongate, and fusiform shapes that may be about 0.2 μm-20 μm in diameterand approximately 20 μm-200 μm in length. In one embodiment, the averagepore diameter 111 may be approximately less than or equal to 30 μm. Forexample, the average pore diameter 111 may be about 0.2-30 μm, or 0.2-2μm.

Further, the pores 110 of the ester-based material may be reticulatedpores. Reticulation refers to the open nature of the pores 110 such thatthe lumen 112 of the pores 110 communicates with adjacent pores 110,such as through channels 113. The struts or edges of the pores 110 wherecontact is made with adjacent pores 110 remain intact in reticulatedfoam. Without being bound by theory, the open-celled and substantiallyuniform pore size of the reticulated absorptive dressing 101 mayfacilitate substantially uniform diffusion of nutrients, oxygen,bioactives, and allow for negative pressure across the entire wound bed120, and efficient removal of exudates upon application of negativepressure wound therapy.

In various embodiments of the present invention, the size of the pores110 of the absorptive dressing 101 including an ester-based material maybe less than the pore size of conventional ester foams and/orsubstantially similar to the diameter of smooth muscle cells 121. In oneembodiment, the pores 110 may be created in an ester-based materialusing any suitable process such as using molds including fiber-opticmolds, stamping methods, bombardment methods such as ion beam orultrasound bombardment, chemical etching, chemical baths, and/or laserirradiation of the ester-based material.

In one embodiment, the pores of conventional ester foam may be reducedto a desired size in any suitable process such as felting. The feltingprocess may include thermal, mechanical, or chemical compression of theester-based material, resulting in permanently compressing the pores110. The felting process may include heating the ester-based materialduring the manufacturing process of the polyurethane ester foam,followed by the application of a degree of compression to produce adesired pore density, a desired fluid dynamic within the foam, and/or anincrease in tensile strength. In various embodiments, the biocompatiblefoam may be processed to obtain any desired physical properties such asany desired pore size, porosity, density, reticulation of pores,permeability and/or tensile strength.

In various embodiments, the ester-based material may be manufacturedand/or further processed to obtain any desired chemical properties suchas affinity for wound fluid, elasticity of the ester-based material toallow contraction of the absorptive dressing 101 under negativepressure, even wound fluid suspension and/or absorption within theester-based material, and/or retention and/or delivery of additives. Insome embodiments, the ester-based material may be customized to promotehealing of a particular type of wound bed 120. For example, a wound bed120 including the smooth muscle fistula 122 of a highly acidic nature,such as a biliary fistula, may benefit from an absorptive dressing 101with an altered chemistry such as impregnation with a neutralizingcomposition such as bicarbonate. In another embodiment, the ester-basedmaterial may include alcohols, antibiotics, pharmaceutically activecompounds, and the like. Accordingly, the chemistry, pore size, and/orthe pore geometry within the absorptive dressing 101 may be optimizedand/or customized to provide a maximum healing benefit to any particulartype of wound bed 120. Additionally, in some embodiments, theester-based material may include a plurality of horizontally arrangedlayers with the desired physical properties that are coupled to form asingle cohesive piece of foam.

In further embodiments, as illustrated in FIGS. 5A-5B, the absorptivedressing may include more than one layer of foam where each layerincludes a substantially uniform pore size and/or pore geometry withineach layer, but has a different pore size and/or pore geometry relativeto an adjacent layer or layers. For example, referring to FIG. 5A, anabsorptive dressing 501 a may have a first layer 540 including pores 541having a diameter that may be larger than the pores 551 of a secondlayer 550. Referring to FIG. 5B, an absorptive dressing 501 b mayinclude the second layer 550 overlaid with the first layer 540 and thefirst layer 540 may be overlaid by an additional second layer 550. Theabsorptive dressing 501 b may include as many alternating layers 540/550as desired. In various embodiments, the pores 541 and 551 may beapproximately the size and/or diameter of the cells with which theabsorptive dressing 501 a, 501 b will be used. For example, the pores551 may be about 0.1 μm to about 10 μm and the pores 541 may be about 10μm to about 100 μm, or about 20 μm to about 100 μm. Accordingly, manypores 541 and/or pores 551 may extend the length of any smooth musclecells in the wound bed 120. However, the pores 541 and 551 may also haveany of the characteristics of the pores 110 discussed above, includingany of a variety of shapes, sizes, diameters or reticulation asdiscussed above.

Without being bound by theory, it is believed that having suchalternative layers of 540 and 550 will create a better seal via thesmaller pores 551 at the wound bed 120 while still allowing for higherlevels of absorption and compressibility (to compensate for peristalsisand other movements by the patient) at the larger pores 541. Inaddition, in the absorptive dressing 501 b, having the second layer 551on both the top and bottom of first layer 540 allows the absorptivedressing 501 b to be reversible, facilitating its use by medicalpersonnel. In such an embodiment, the pores 551 may be about 0.1 μm toabout 50 μm and the pores 541 may be about 10 μm to about 300 μm. Insome embodiments, the first layer 540 may have a thickness of about 0.1mm to about 2 mm and the second layer 550 may have a thickness between 2mm and 8 mm.

Referring to FIG. 5C, describing another embodiment of the absorptivedressing, in an absorptive dressing 501 c, the pores 541 and the pores551 may be combined within the same layer, such as a layer 560. Forexample, smaller pores 551 may be interspersed between larger pores 541where each pore 551 is surrounded by larger pores 541. Additionally, theabsorptive dressing 501 c may include pores having a limitedreticulation to reduce the volume and/or rate of wound fluid flowthrough the absorptive dressing 501 c. The pores of layer 501 c may alsohave any of the characteristics of the pores 110 discussed above,including any of a variety of shapes, sizes, diameters or reticulationas discussed above. For example, the pores of layer 560 may have a sizeof about 0.1 μm to about 300 μm.

Without being bound by theory, by interspersing different sized pores,it is believed that the wound fluid would travel through pathwaysincluding large pores 541 and smaller pores 551, increasing theresistance to fluid flow. In some embodiments, the interspersion ofsmall pores 551 with large pores 541 may increase the resistance of theabsorptive layer 501 c to wound fluid, creating a tighter seal over thewound bed 120 as compared to an absorptive layer having a uniform orlarger pore 541 structure. This tight seal or layer of pressureresistance may lead to lower wound fluid production and output from thewound bed 120 and/or increased wound fluid flow back through the sourceof the fistula, such as an intestine. Additionally, without being boundby theory, it is believed that selection of the size of small pores 551and/or large pores 541 may provide a filtration function to facilitateremoval of pre-selected particles from the wound fluid while encouraginglower wound fluid production and/or redirection of flow. For example,the size of small pores 551 and/or large pores 541 may be similar to thesize of various cell debris and/or bacteria, which are generallysubstantially smaller than eukaryotic cells.

Layer 560 may include the entire absorptive dressing 501 c, or may belayered with additional layers having interspersed large and small poresor may be layered with additional layers of uniform pores, such as firstand second layers 501 a and 501 b. In further embodiments, any ofabsorptive dressings 501 a, 501 b and 501 c may be layered with a foamhaving a larger pore size, such as conventional foams having a pore sizebetween 100 μm-600 μm. In addition, any of absorptive dressings 501 a,501 b and 501 c may have the physical and chemical properties of thevarious embodiments of absorptive dressings discussed herein, forexample, the absorptive dressing 101.

In various embodiments, the absorptive dressing including horizontallystacked layers, such as the layers 540, 550 and 560, may include ajunction 545 between two adjacent layers, as shown in FIG. 5A. Thejunction 545 may be treated with any suitable additive to provide orimprove a desired physical and/or chemical property of the absorptivelayer 501 a, 501 b, 501 c. For example, a solution including one or moreadditives may be painted, sprayed, wiped, sponged, or otherwise appliedto the junction 545. The additives may include biocompatible materialsuch as an antibacterial agent, a pharmaceutically active agent, avitamin, a semi-occlusive substance, an emollient, a humectant,medicament, and the like. The absorptive dressing 501 a, 501 b, 501 cmay be soaked and/or saturated in the additive prior to or upon itsapplication onto the wound bed 120.

The method or use for the absorptive dressings 501 a, 501 b and 501 c isthe same as the method of use for the embodiment of FIG. 1. However, inembodiments in which the absorptive dressings 501 a, 501 b and 501 c arenot reversible, i.e., in which the outermost layers of the absorptivedressings 501 a, 501 b and 501 c have different pore sizes, theoutermost layer with the smallest pore size may face the wound bed inorder to create a tighter seal over the wound bed 120.

In further embodiments, additional structural features (which may alsobe referred to as secondary structural features whereas the pores of theabsorptive dressing may be referred to as primary structural features)may be introduced into the absorptive dressing to encourage woundclosure by directional wound fluid flow through the absorptive dressing.Such structural features may direct wound fluid flowing from the edges125 of the wound bed 120, particularly the edges 626 of the fistula 122,toward a central area above the fistula 122 to promote a pull of thetissues toward a midline of the fistula 122. Conventional absorptivedressings, such as ether-based foams, do not discretely or intentionallyemploy structural features that influence or guide the direction ofwound fluid through the absorptive dressing. Any suitable method forcreating directional fluid flow may be implemented within the absorptivedressing.

In one embodiment, an example of which is illustrated in FIG. 6, thestructural features may direct wound fluid flowing from the edges 125 ofthe wound bed 120, particularly the edges 626 of the fistula 122 towardthe center of an absorptive dressing 601 to promote a pull of thetissues toward a midline of the fistula 122. The absorptive dressing 601may have the physical and chemical properties of the various embodimentsof absorptive dressings discussed herein, for example, the absorptivedressings 101, 501 a, 501 b and 501 c. The absorptive dressing 601 mayalso include preformed flow paths 614 of large diameter pores through ascaffold 615 of small diameter pores to encourage wound fluid toprimarily move through the preformed flow paths 614. The preformed flowpaths 614 may include pores having one or more diameters different fromthe pore size(s) of the scaffold 615 (e.g., greater than the pore sizeof the scaffold) or may include hollow pathways, e.g., from the side ofthe absorptive dressing 601 closest to the wound bed 120 to the oppositeside farthest from the wound bed 120. The preformed flow paths 614 maybe arranged in an hourglass-like shape, such as an a top heavy hourglassshape as shown in FIG. 6, or the preformed flow paths 614 may have asymmetrical or bottom-heavy hourglass-like shape. The hourglass-likeshape may be three-dimensional, such that a cross-section of theabsorptive dressing 601 in a horizontal direction may show the preformedflow paths 614 as circles of different sizes corresponding to the levelof the hourglass-like shape at which the cross-section is taken. Infurther embodiments, the preformed flow paths 614 may have a cone-shape,with the larger opening of the cone-shape facing the fistula 122. Insuch embodiments, the smaller opening or apex of the cone-shape may facethe vacuum pump 134 located above it.

In some embodiments, more than one vacuum pump 134 may be included, forexample, two to five vacuum pumps 134, at the upper ends 616 of thepreformed flow paths 614. Alternatively, a vacuum pump capable ofcreating a circular negative pressure flow above the upper ends 616 ofthe preformed flow paths 614 can be used. The lower ends 617 of thepreformed flow paths 614 may be positioned between the edges 626 of thefistula 122 so that the negative pressure of the vacuum pump 134 directsthe fluid flow and the edges 626 of the fistula 122 inwardly to aid inthe closure of the fistula 122. Prior to use, the absorptive dressing601 may be cut in order to have the lower ends 617 of the preformedpaths 614 correctly sit between the edges 626 of the fistula 122.Without being bound by theory, it is believed that in use, negativepressure created by the vacuum pumps 134 may pull both the wound fluidand the edges 626 of the fistula 122 upwards and because of the lowerpressure of the preformed flow paths 614, the wound fluid and the edges626 will be pulled towards the preformed flow paths 614. Thedirectionality of the movement of the edges 626 will aid in the closureof the fistula 122. Further, as the edges 626 of the fistula 122 growcloser together, a further embodiment of the absorptive dressing 601 canbe used in which lower ends of the preformed flow paths 614 arepositioned closer together than in previously used absorptive dressing601, so that the edges 626 of the fistula 122 are still being directedinwardly during the use of the vacuum pumps 134. This process can berepeated until the fistula is closed or until the edges of the fistulaare too close together for preformed flow paths to create an inwardpull.

In use, the absorptive dressing 601 including the preformed flow paths614 may be applied to the wound bed 120 including the smooth musclefistula 122. The absorptive dressing 601 may be positioned such that thelower ends 617 of the preformed flow paths 614 are between the edges 626of the fistula 122. An occlusive material 130 may be overlaid on theabsorptive dressing 601 such that it fully covers the edges 125 of thewound bed 120. Medical personnel may exert pressure on the occlusivematerial 130 until it adheres to the skin 124 and creates an airtightseal over the wound bed 120. The adapter 131 may be connected to asource of negative pressure, for example, a vacuum pump 134. The vacuumpump 134 may be assembled with the vacuum tube connector 132 and thevacuum tube 133 in order to connect to the adapter 131. However, morethan one set of the vacuum pumps 134, vacuum tube connectors 132, thevacuum tubes 133 and adapters 131 may be assembled as shown in FIG. 6.The adapter 131 may be connected to the access point in the occlusivematerial 130 to allow negative pressure to flow from the vacuum pump 134to the absorptive dressing 601. If more than one vacuum pump 134 isused, each adapter 131 associated with each vacuum pump 134 may have itsown access point in the occlusive material 130. Upon activating thevacuum pump 134, negative pressure may be applied to the absorptivedressing 601 thereby withdrawing wound fluid from the absorptivedressing 601 and the wound bed 120. Without being bound by theory,negative pressure created by the vacuum pump or vacuum pumps 134 maypull both the wound fluid and the edges 626 of the fistula 122 upwardsand towards the preformed flow paths 614.

Other embodiments, as shown in FIGS. 7A-7B, may include structuralfeatures that create pressure gradients and/or physical barriers todirect fluid flow. Such structural features may include barriers 770composed of plastic, metal or other materials, such as biocompatiblematerials. However, because the barriers 770 may be incorporated into anabsorptive layer 701 and not in direct contact with tissue,non-biocompatible materials may also be used. The absorptive dressing701 may have the physical and chemical properties of the variousembodiments of absorptive dressings discussed herein, for example, theabsorptive dressings 101, 501 a, 501 b and 501 c.

The barriers 770 may have a wing-like shape, such as an airplanewing-shape. For example, as shown in FIG. 9C, the barriers 770 may beasymmetrical along a chord line 771 connecting the leading edges 772 andthe trailing edges 773 of the barriers 770 creating a camber in whichthe inner portions 774 of the barriers 770 have a thickness t₁ greaterthan the thickness t₂ of the outer portions 775 of the barriers 770. Theinner portions 774 are directed towards an area of the absorptivedressing 701 above the center of the fistula 122 and the outer portions775 are directed away from the area of the absorptive dressing 701 abovethe center of the fistula 122. The leading edges 772 may also have anangle of attack α relative to the direction of fluid flow 776 from thefistula 122. Without being bound by theory, it is believed that thewing-like shape of the barriers 770 and the angle of attack α takeadvantage of the Bernoulli Principle to create a pressure gradient inwhich the pressure between the inner portions 774 of the barriers 770 islower than the pressure surrounding the outer portions 775 of thebarriers 770. With the application of negative pressure from the vacuumpump 134, wound fluid flowing from the fistula 122 along with the edges626 of the fistula 122 will be directed towards the area of low pressurebetween the inner portions 774, constricting the opening of the fistulaand aiding in wound closure.

The barriers 770 may be a single piece structure or multiple pieces. Forexample, the barriers 770 may be a single and/or monolithic donut-shapedstructure when viewed from above or the barriers 770 may be multipleoverlapping wings arranged in a circle around the area above the fistula122. In further embodiments, the barriers 770 may vary in size. Withoutbeing bound by theory, it is believed that by varying the size of thebarriers 770, for example, incrementally from small to large around thecircumference of the barriers 770, the directionality of the fluid flowcan be controlled.

The barriers 770 may have a height from the leading edges 772 to thetrailing edges 773 of about 5 mm to about 40 mm. In some embodiments,the barriers 770 may have a height from the leading edges 772 to thetrailing edges 773 of about 10 mm to about 30 mm. The barriers 770 mayhave a width, including the thickness t₁ of the inner portions 774 andthe thickness t₂ of the outer portions 775, of about 1 mm to about 10mm. In some embodiments, the barriers 770 may have a width, includingthe thickness t₁ of the inner portions 774 and the thickness t₂ of theouter portions 775, of about 1 mm to about 3 mm.

In use, the absorptive dressing 701 including the barriers 770 may beapplied to the wound bed 120 including the smooth muscle fistula 122.The absorptive dressing 701 may be positioned such that the leadingedges 772 of the barriers 770 are above or between the edges 626 of thefistula 122. An occlusive material 130 may be overlaid on the absorptivedressing 701 such that it fully covers the edges 125 of the wound bed120. Medical personnel may exert pressure on the occlusive material 130until it adheres to the skin 124 and creates an airtight seal over thewound bed 120. The adapter 131 may be connected to a source of negativepressure, for example, a vacuum pump 134. The vacuum pump 134 may beassembled with the vacuum tube connector 132 and the vacuum tube 133 inorder to connect to the adapter 131. The adapter 131 may also beconnected to the access point in the occlusive material 130 to allownegative pressure to flow from the vacuum pump 134 to the absorptivedressing 701. Upon activating the vacuum pump 134, negative pressure maybe applied to the absorptive dressing 701 thereby withdrawing woundfluid from the absorptive dressing 701 and the wound bed 120. Withoutbeing bound by theory, negative pressure created by the vacuum pump 134may pull both the wound fluid and the edges 626 of the fistula 122upwards and towards the area between the inner portions 774 of thebarriers 770.

Further embodiments, examples of which are shown in FIGS. 8A-8D, mayinclude structural features including suitable devices for drawing inwound fluid from the wound bed 120 in an upward and spiral pattern thatmay promote lifting and, at the same time, gentle twisting of thetissues in the wound bed 120. The lifting and twisting motion of thetissue as wound fluid is withdrawn through the device may furtherencourage the wound edges to be drawn together toward the midline of thewound bed 120 and promote ultimate wound closure. As shown in FIG. 8A,the structural features may include a radial housing 880 that may beincorporated into an absorptive dressing 801. The absorptive dressing801 may have the physical and chemical properties of the variousembodiments of absorptive dressings discussed herein, for example, theabsorptive dressings 101, 501 a, 501 b and 501 c. The radial housing 880may be positioned such that a central axis C of the radial housing 880is above the center of the fistula 122. The radial housing 880 mayinclude a substantially hour-glass shaped hollow structure.Alternatively, the radial housing 880 may include one or more tubesspirally wound to form a cone-shaped structure where the larger openingof the cone-shaped structure faces the fistula 122. Without being boundby theory, it is believed that by virtue of its shape and structure, theradial housing 880 is capable of spinning a fluid moving through theradial housing 880 at a suitable pressure. The fluid may include a gas,a liquid or a combination of both. For example, the fluid may includefiltered air and/or saline.

In some embodiments, the fluid may be delivered into the radial housing880 under pressure through a delivery tubing 885, such as by an aircompressor, or by creating a twisted Venturi effect where wound fluidmoving through a central area 886 of the radial housing 880 draws gasthough the delivery tubing 885 by a vacuum pressure. The radial housing880 may include a radial tubing 881 that is capable of receiving thefluid from the adjacent delivery tubing 885. The fluid may then bedelivered from the radial tubing 881 into the central area 886 of theradial housing 880 via injection ports 887. The central area 886 may bedefined by the radial tubing 881 of the radial housing 880. Theinjection ports 887 may have varied diameters along the length and/orheight of the radial housing 880 to promote the rotation and upwardforce of the wound fluid and resultant toroidal twist of the tissue. Forexample, the injection ports 887 may be larger at the inferior opening882 and smaller at the flow constriction zone 883. Alternatively, theinjection ports 887 may be smaller at the inferior opening 882 andlarger at the flow constriction zone 883. In addition, the walls 888 ofthe injection ports 887 may be angled to direct the flow of the fluid.The walls 888 of the injection ports 887 may be angled such that thefluid is directed to the center of the central area 886.

In some embodiments, the radial housing 880 may include a singlecontinuous radial tubing 881, as shown in FIG. 8B, or may includemultiple pieces of radial tubing coupled together. The radial tubing 881may include a flexible, biocompatible, and/or biodegradable material.For example, the radial tubing 881 may include a polymeric materialwhere each layer of the radial tubing 881 may be flexible in relation toadjacent layers and/or may be flexible in relation to its contact withthe wound bed 120 to provide for patient ambulation. In one embodiment,each layer of the radial tubing 881 may be offset as the radial tubing881 ascends to achieve the hourglass shape. Accordingly, the radialhousing 880 may include at least three blended zones, each of which mayhave a different diameter. For example, the three blended zones mayinclude at least an inferior opening 882, a superior opening 884, and aflow constriction zone 883.

In some embodiments, the wound fluid may enter the central area 886 ofthe radial housing 880 from the wound bed 120 (including the smoothmuscle fistula 122), through the inferior opening 882, and may exit thesuperior opening 884 to the vacuum pump 134. However, in someembodiments, the radial housing 880 may be symmetrical such that eitherthe inferior opening 882 or the superior opening 884 may function as thefluid inlet or outlet. Accordingly, either end of the radial housing 880may be applied to the wound bed 120. In such embodiments, as shown inFIG. 8C, the side of the radial housing 880 facing downward and touchingthe wound bed 120 may function as the inferior opening 882 and the sidefacing upward toward the vacuum source including the vacuum tube 133 mayfunction as the superior opening 884.

In some embodiments, the delivery tubing 885 may have valves, forexample, one-way valves, such as butterfly valves or valves similar infunction and/or structure to a revolving door, for preventing a reversalof flow. In other embodiments, the radial housing 880 may have one-wayvalves at the delivery tubing 885 to prevent wound fluid from exuding upinto the vacuum tube 133 or vacuum pump 134 after the vacuum pump 134 isturned off.

As also shown in FIG. 8C, in some embodiments, the walls 888 of theinjection ports 887 may be angled such that the fluid is directed to thecenter of the flow constriction zone 883. However, for the injectionports 887 closest to the inferior opening 882, the injection ports 887may be angled perpendicular to the central axis C of the radial housing880 in order to push the fluid towards the central axis C of the radialhousing 880 and resultantly push the edges 626 of the fistula 122 closertogether.

In some embodiments, as shown in FIG. 8D, the walls 888 of the injectionports 887 may be angled in a circumferential direction. Without beingbound by theory, it is believed that by angling the injection ports 887in a circumferential direction, the fluid will be rotated in a helicalpattern up the radial housing resulting in a toroidal twist of the fluidand of the edges 626 of the fistula 122 facilitating closure of thefistula 122.

In various embodiments of the present invention, the radial housing 880may comprise a flexible, biodegradable material that may be compressedunder the negative pressure provided by the vacuum pump 134. Forexample, the radial housing 880 may be made of a composition that candissolve, such as sugar crystals and/or a chromic gut polymer. In someembodiments, one or more additives may optionally be applied to theinside of the radial housing 880 to interact with the wound fluidentering through the inferior opening 882. For example, the additivesmay optimize at least one of the adhesion or cohesion of the wound fluidas it travels through the radial housing 880 and may encourage thetoroidal twist of the wound fluid. In some embodiments, additives may beadded to facilitate or slow the rate of dissolution of the radialhousing 880, depending the desired resulted in view of thecharacteristics of the fistula 112. For example, for a radial housing880 made of sugar crystals, additives may be added to slow the rate ofdissolution so that the dissolution of the radial housing 880 correlateswith the rate of wound healing.

In some embodiments, the radial tubing 881 may taper in diameter towardthe flow constriction zone 883. In other embodiments, the diameter ofthe radial tubing 881 may remain constant or may increase toward theflow constriction zone 883. The radial tubing 881 may have a diameterbetween about 0.5 mm and about 5 mm. The injection ports 887 may becircular in shape and have a diameter of about 0.1 mm to about 0.7 mm.However, the injection ports 887 need not be circular and may have anyother geometric shape.

The radial housing may have a diameter at the inferior opening 882sufficient to completely encircle the fistula 122. For a stomatizedfistula, the radial housing may have a diameter at the inferior openingsufficient to completely encircle the fistula 122 including thestomatized walls surrounding the fistula. For example, the radialhousing 880 may have a diameter of about 10 mm to about 40 mm. In someembodiments, the radial housing 880 may have a diameter of about 15 mmto about 25 mm.

In further embodiments, the radial tubing 881 of the radial housing 880may be a single hourglass shaped structure. For example, the radialtubing 881 may include a double-walled structure that receives fluidfrom the delivery tubing 885 and have injection ports on the inner paneof the double-walled structure so that the fluid can enter the centralarea 886.

The delivery tubing 885 may be a single tube on one side of the radialhousing 880, or it may be multiple tubes on opposite sides of the radialhousing 880, as shown for example in FIGS. 8C-8D. The delivery tubing885 may include two or more tubes spaced around the periphery of theradial housing 880. Alternatively, the radial housing 880 may be adouble-walled hollow cylindrical structure surrounding the radialhousing 880 and capable of delivering fluid around the entirecircumference of the radial housing 880 at the inferior opening 882. Thedelivery tubing 885 may have a diameter similar to the radial tubing 881of the radial housing 880. For example, the delivery tubing 885 may havea diameter between about 0.5 mm and about 5 mm.

In use, the absorptive dressing 801 including the radial housing 880 maybe applied to the wound bed 120 including the smooth muscle fistula 122.The absorptive dressing 801 may be positioned such that the inferioropening 882 of the radial housing 880 encircles the fistula 122. Anocclusive material 130 may be overlaid on the absorptive dressing 601such that it fully covers the edges 125 of the wound bed 120. Medicalpersonnel may exert pressure on the occlusive material 130 until itadheres to the skin 124 and creates an airtight seal over the wound bed120. The adapter 131 may be connected to a source of negative pressure,for example, a vacuum pump 134. The vacuum pump 134 may be assembledwith the vacuum tube connector 132 and the vacuum tube 133 in order toconnect to the adapter 131. The adapter 131 may also be connected to theaccess point in the occlusive material 130 to allow negative pressure toflow from the vacuum pump 134 to the absorptive dressing 801. Uponactivating the vacuum pump 134, negative pressure may be applied to theabsorptive dressing 801 thereby withdrawing wound fluid from theabsorptive dressing 801 and the wound bed 120. Without being bound bytheory, negative pressure created by the vacuum pump 134 may pull boththe wound fluid and the edges 626 of the fistula 122 upwards and towardsthe central area 886.

Referring to FIG. 9, in some embodiments of the present invention, anegative pressure treatment system 900 may further include a wound bedinterface layer 902 between the absorptive dressing 101 and the woundbed 120. The interface layer 902 may be used with any of the embodimentsof the absorptive dressings 101, 501 a, 501 b, 501 c, 601, 701 and 801described above. The wound bed interface layer 902 can be a healinglayer having an affinity for living tissue and/or wound fluid producedby the wound. The interface layer 902 may form chemical interactions,such as chemical bonds and/or attractions, with the tissue in the woundbed 120 at the interface of the interface layer 902 and the wound bed120. In one embodiment, the interface layer 902 may form a “chemicalseal” where the chemical interactions effectively promote closure of thewound bed 120. Closure of the wound bed 120 may reduce or eliminate theflow of wound fluid out of the wound bed 120. For example, where thewound bed 120 includes an enteric fistula as the smooth muscle fistula122, the flow of intestinal material out of the wound bed 120 may slowand ultimately stop due to the chemical seal.

In some embodiments, the interface layer 902 may provide normalizationof negative pressure at the wound bed 120. The vertical distribution ofnegative pressure through the absorptive dressing 101 between the sourceof vacuum pressure at the occlusive material 130 and the bottom of theabsorptive dressing 101 that contacts the wound bed 120 or the interfacelayer 902 may be variable depending on the thickness of the absorptivedressing 101. Application of the interface layer 902 between theabsorptive dressing 101 and the wound bed 120 may enhance fluidmanagement of exudate from the wound bed 120 by creating a uniform layerof negative pressure at the wound bed 120. The uniformity of pressureprovided by the interface layer 902 may improve closure of difficult toclose wounds such as stomatized wounds where the inner walls of thewound may become thickened and may resist closure.

In various embodiments, the interface layer 902 may be placed over thesmooth muscle fistula 122 in the wound bed 120. The absorptive dressing101 may then be placed over the interface layer 902. In variousembodiments, the interface layer 902 may be at least partially coupledto the absorptive dressing 101. In some embodiments, the interface layer902 may include an ester-based material, for example an ester-basedmaterial with the physical and chemical properties discussed above withregards to the absorptive dressing 101. In one embodiment, the interfacelayer 902 may include a bio-absorbable material. The bio-absorbablematerial may include a hydrophilic material that may have an affinity tothe tissue of the smooth muscle fistula 122. In one embodiment, thebio-absorbable material may include a suture material such as absorbablesurgical plain gut suture. Plain gut suture is composed of purifiedconnective tissue and may absorb in the body within a few days byenzymatic dissolution as part of the body's response to a foreignobject. In some embodiments, the bio-absorbable material may include alonger lasting absorbable material that dissolves more slowly than plaingut sutures, such as chromic gut sutures or Vicryl™. The ester-basedmaterial and/or the bio-absorbable material may resist tissue ingrowthfrom the smooth muscle fistula 122.

In another embodiment, the interface layer 902 may include a hydrophobicnon-absorbable material. For example, the hydrophobic material maycomprise a petroleum emulsion such as Adaptic® or a silicone wounddressing such as Mepitel®. Such hydrophobic material may also resisttissue ingrowth from the smooth muscle fistula 122.

In some embodiments, the interface layer 902 may be a thin sheet havinga thickness. In one embodiment, the thickness may be about the thicknessof a sheet of printer paper, such as about 100 μm. The interface layer902 may include a plurality of pores to allow wound fluid produced bythe wound bed 120 to flow through the interface layer 902 and into theabsorptive dressing 101. The diameter of the pores may be similar to thewidth/diameter of smooth muscle cells, such as between about 1 μm toabout 20 μm. In one embodiment, the interface layer 902 may include asingle layer of pores. In some embodiments, the interface layer 902 mayinclude more than one layer of pores where each layer includes asubstantially uniform pore size and/or pore geometry within each layer,but a different pore size and/or pore geometry than an adjacent layer orlayers. For example, the interface layer 902 may include a layerstructure and/or pore structure as described with reference to theabsorptive dressings 501 a, 501 b and 501 c and FIGS. 5A-5C above. Forexample, the interface layer 902 may include multiple alternating layersin which the layers between layers of smaller pore size and larger poresize, such as discussed regarding FIGS. 5A-5B. In various embodiments,the smaller pores may be about 1 μm to about 10 μm and the larger poresmay be about 10 μm to about 20 μm. In some embodiments, the interfacelayer 902 may include a layer with larger pores sandwiched between twosmaller pore layers, such as described with reference to FIG. 5C. Thisconfiguration provides for a reversible interface layer 902 which mayfacilitate use by medical staff. The interface layer 902 may also havesmaller pores interspersed between larger pores as described withrespect to FIG. 5C above. Additionally, the interface layer 902 of thisembodiment may include pores having a limited reticulation to reduce thevolume and/or rate of wound fluid flow through the interface layer 902.In embodiments in with the interface layer 902 has multiple layers, thetotal width of all layers of the interface layer 902 combined may beabout 100 μm. In some embodiments, the interface layer 902 may be a thinfilm or sheet having a thickness.

In use, the interface layer 902 may be applied to the wound bed 120including the smooth muscle fistula 122 prior to application of any ofthe embodiments of the absorptive dressings 101, 501 a, 501 b, 501 c,601, 701 and 801 described above.

EXAMPLE 1

A female patient diagnosed with Crohn's disease was hospitalized havingthree enterocutaneous fistulas at the biliary junction. Variousconventional treatments were attempted, but her fistulas persisted,having a fluid drainage rate of 1000-2000 ml per day. The patient wasinformed that her body would not heal this fistula on its own and wasdeclared terminal. The patient agreed to an experimental procedure inwhich an ester-based foam was placed directly on the fistulas. Theester-based foam was composed of reticulated polyurethane ester foamwith a pore size of 133-600 μm sold under the trade name V.A.C. VeraFloCleanse™ Dressing by Kinetic Concepts, Inc. The ester-based foam wasfelted such that the size of the pores varied directionally within thefoam, where the pore size was greater along the length of the foam thanalong the direction of felting (i.e. the thickness). The foam was placeddirectly on the fistulas, with the width of the ester-based foamperpendicular to the fistulas and a flat surface of the ester-foam indirect contact with the fistula, covered with an occlusive material andattached to a vacuum pump via a vacuum tube, as exemplified in FIG. 1. Asecond vacuum tube and pump was positioned at the opposite end of thewound from the fistulas to collect exuded drainage fluid not collectedby the first vacuum pump. The ester-based foam was replaced every threedays. Within about 12 hours of the experimental procedure, the fluiddrainage had decreased to a rate of approximately 500 ml/day. In theproceeding days, the fluid drainage decreased to approximately 200ml/day. In addition, the overall coloration, texture and smell of thewound improved within three days. The tissue at the wound bed improvedfrom a yellowish slough-covered tissue to a red, beefy granular tissue.In addition, likely do to the decrease in fluid drainage, the smell ofbile at the wound site decreased within the first three days of theexperimental procedure as well.

In the foregoing description, the invention has been described withreference to specific embodiments. Various modifications and changes maybe made, however, without departing from the scope of the presentinvention as set forth. The description and figures are to be regardedin an illustrative manner, rather than a restrictive one and all suchmodifications are intended to be included within the scope of thepresent invention. Accordingly, the scope of the invention should bedetermined by the generic embodiments described and their legalequivalents rather than by merely the specific examples described above.For example, the steps recited in any method or process embodiment maybe executed in any appropriate order and are not limited to the explicitorder presented in the specific examples. Additionally, the componentsand/or elements recited in any system embodiment may be combined in avariety of permutations to produce substantially the same result as thepresent invention and are accordingly not limited to the specificconfiguration recited in the specific examples.

For example, while certain embodiments of the methods and systemsdescribed above disclose the withdrawal of body fluid withoutintroducing any other fluid in order to promote healing, suchembodiments may be modified to optionally introduce a carrier fluid suchas air, water, saline, or other solutions or fluids into the wound tofurther encourage a desired flow of body fluid, and thereby promotehealing.

Benefits, other advantages and solutions to problems have been describedabove with regard to particular embodiments. Any benefit, advantage,solution to problems or any element that may cause any particularbenefit, advantage or solution to occur or to become more pronounced,however, is not to be construed as a critical, required or essentialfeature or component.

Other combinations and/or modifications of the above-describedstructures, arrangements, applications, proportions, elements, materialsor components used in the practice of the present invention, in additionto those not specifically recited, may be varied or otherwiseparticularly adapted to specific environments, manufacturingspecifications, design parameters or other operating requirementswithout departing from the general principles of the same.

The present invention has been described above with reference tospecific embodiments. However, changes and modifications may be made tothe above embodiments without departing from the scope of the presentinvention. These and other changes or modifications are intended to beincluded within the scope of the present invention.

The invention claimed is:
 1. A method of treating a wound bed includinga smooth muscle fistula without causing substantial cellular disruptionor damage, the method comprising: applying an absorptive dressingcomprising an ester-based foam having pores with a width of about 0.1 μmto about 80 μm directly to the wound bed including the smooth musclefistula; and applying a negative pressure to the absorptive dressing tothereby withdraw wound fluid from the wound bed.
 2. The method of claim1, further comprising applying an occlusive material over the absorptivedressing to form a seal at the wound bed.
 3. The method of claim 1,wherein the absorptive dressing comprises secondary structural featureswithin the ester-based foam and adapted to impart a flow pattern to thewound fluid being withdrawn from the wound bed.
 4. The method of claim1, wherein the ester-based foam comprises at least two layers andwherein a first layer has an average pore size greater than an averagepore size of a second layer.
 5. The method of claim 1 wherein theester-based foam has pores with a width of about 0.1 μm to about 50 μm.6. A negative pressure treatment system for the treatment of a wound bedincluding a smooth muscle fistula, the negative pressure treatmentsystem comprising: an absorptive dressing comprising an ester-based foamadapted to be placed directly against the wound bed and to contactsmooth muscle without causing substantial cellular disruption or damagein the negative pressure environment, the foam having primary structuralfeatures comprising pores with a width of about 0.1 μm to about 50 μmand secondary structural features adapted to direct a flow of woundfluid from the wound bed; a vacuum pump configured to apply negativepressure to the absorptive dressing to thereby withdraw wound fluid fromthe wound bed; and an interface layer adapted to be placed between theabsorptive dressing and the wound bed.
 7. The negative pressuretreatment system of claim 6, wherein the interface layer comprises anester-based material.
 8. The negative pressure treatment system of claim7, wherein the interface layer comprises a film having pores with awidth of about 0.1 μm to about 50 μm.
 9. A negative pressure treatmentsystem for the treatment of a wound bed including a smooth musclefistula, the negative pressure treatment system comprising: anabsorptive dressing comprising an ester-based foam layer; an interfacelayer adjacent to the absorptive dressing; wherein the absorptivedressing is adapted to be placed directly against the wound bed, and theinterface layer is adapted for contacting smooth muscle without causingsubstantial cellular disruption or damage in the negative pressureenvironment, the foam having primary structural features comprisingpores with a width of about 0.1 μm to about 50 μm and secondarystructural features adapted to direct a flow of wound fluid from thewound bed; and a vacuum pump configured to apply negative pressure tothe absorptive dressing to thereby withdraw wound fluid from the woundbed.
 10. The negative pressure treatment system of claim 9, wherein theinterface layer comprises an ester-based material.
 11. The negativepressure treatment system of claim 10, wherein the interface layercomprises a film having pores with a width of about 0.1 μm to about 50μm.